Progress 03/10/00 to 03/09/05
Outputs
Botrytis cinerea is a ubiquitous pathogen of many greenhouse-grown crops. Non-chemical alternatives to fungicides, which would fit into an IPM strategy for Botrytis blight, are needed. An alternative to traditional chemicals is the use of biological control with yeasts. Epiphytic yeasts displayed biocontrol activity against B. cinerea on geranium seedlings and leaf disks. The two assays were found to be highly correlated; infection by the fungus and yeast biocontrol activity against B. cinerea on leaf disks and seedlings was comparable. The ability of yeasts to attach to B. cinerea is presumed to contribute to biocontrol activity. 292 yeasts were screened for their ability to attach to conidia of B. cinerea; some attachment ability was observed with all isolates. Ten fungicides were tested for their effect on yeast biological control activity. Azoxystrobin, trifloxystrobin and vinclozolin enhanced yeast biocontrol activity against B. cinerea on geranium seedlings.
Different rates of vinclozolin with yeast resulted in an effective, consistent level of control not observed with the yeast alone against an isolate of B. cinerea resistant to vinclozolin. We further tested the yeast/vinclozolin mixture against ten additional isolates of B. cinerea resistant to vinclozolin. Variability in biocontrol efficacy against most of the isolates was reduced by the addition of vinclozolin. Large populations of yeasts are required for biological control on leaf surfaces. The effects of fungicides on population size and the development of fungicide resistance in the phylloplane yeast flora of bentgrass was investigated. In spring of 2001, four fungicides were applied separately over a six week period to creeping bentgrass (Agrostis palustris). Total yeast populations in the fungicide treated plots were significantly lower than the check plots on 3 out of 4 sample dates. In the fall, azoxystrobin or propiconazole were applied twice to the bentgrass over three
weeks. Significantly larger total yeast populations were observed compared to resistant or highly resistant populations for each treatment on every sample date. Total yeast populations were significantly higher in the check plots compared to either the propiconazole or azoxystrobin treated plots on the first 3 of 5 sample dates. Yeasts (N=114) with no prior exposure to fungicides were more sensitive to chlorothalonil, propiconazole, flutolanil, and iprodione than a second group (N=115) isolated from fungicide treated turfgrass. These results suggest that fungicide resistance among phylloplane yeasts is widespread and could be an important factor in the development of biological control agents for turfgrass diseases. Additional factors that were observed to affect yeast communities on turfgrass include the presence of disease. In general, healthy and diseased bentgrass leaves supported larger yeast communities than healthy or diseased tall fescue leaves. Total yeast communities on
Sclerotinia homoeocarpa-infected or Rhizoctonia solani-infected bentgrass leaves were 3.6 to 10.2 times and 6.2 to 6.4 times larger, respectively, than the communities on healthy leaves.
Impacts
Recently it was suggested that recommendations for managing Botrytis blight on ornamental crops in greenhouses in the Southeastern U.S. should de-emphasize the use of thiophanate-methyl, vinclozolin, and chemically related compounds due to the low incidence of isolates still sensitive to these fungicides. Use of yeast biocontrol in conjunction with vinclozolin could potentially allow for continued or even increased use of this fungicide on ornamental crops. The enhancement of yeast biocontrol activity by vinclozolin needs to be further tested against additional B. cinerea isolates, in scaled-up greenhouse trials with natural populations of the pathogen, and on different ornamental crops.
Publications
- Allen, T.W., Burpee, L.L, and Buck, J.W. 2004. In vitro attachment of phylloplane yeasts to Botrytis cinerea, Rhizoctonia solani and Sclerotinia homoeocarpa. Canadian Journal of Microbiology 50: In press.
- Allen, T.W, Quayyum, H.A., Burpee, L.L, and Buck, J.W. 2004. Effect of foliar disease on the epiphytic yeast communities of creeping bentgrass and tall fescue. Canadian Journal of Microbiology 50:853-860.
- Andrews, J.H., and Buck, J.W. 2002. Adhesion of yeasts to leaf surfaces. In Phyllosphere Microbiology. Edited by S.E. Lindow, E.I. Hecht?Poinar, and V.J. Elliot. APS Press, Minneapolis, MN. pp. 53?68.
- Buck, J.W. 2002. In vitro antagonism of Botrytis cinerea by phylloplane yeasts. Can. J. Bot. 80:885-891.
- Buck, J.W., and Burpee, L.L. 2002. The effects of fungicides on the phylloplane yeast populations of creeping bentgrass. Canadian Journal of Microbiology 48:522-529
- Buck, J.W., and Jeffers, S.N. 2004. Effect of pathogen aggressiveness and vinclozolin on biocontrol efficacy of Rhodotorula glutinis PM4 against Botrytis cinerea on geranium leaf disks and seedlings. Plant Dis. 88:1262-1268.
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Progress 01/01/03 to 12/31/03
Outputs
Ten fungicides used to manage Botrytis blight on ornamental plants were evaluated for their effect on biocontrol of B. cinerea on geranium seedlings by phylloplane yeasts. Lesion development by B. cinerea on geranium cotyledons was significantly reduced by Rhodotorula glutinis PM4 and further reduced by a combination of the yeast and either azoxystrobin or trifloxystrobin at one-tenth (7.5 micrograms active ingredient/ml) or full label rates (75.0 micrograms a.i./ml). Vinclozolin at 250 or 500 micrograms a.i./ml combined with R. glutinis PM4 significantly reduced lesion development by the vinclozolin-resistant isolate of B. cinerea. Thiophanate methyl negatively affected yeast biocontrol activity. Enhanced biocontrol activity with vinclozolin was observed with R. glutinis PM4 at concentrations of 5 x 10+5 and 1 x 10+6 cells/ml, but not 1 x 10+5 cells/ml, when co-inoculated with B. cinerea at 1 x 10+5 conidia/ml. Enhancement of biocontrol activity by vinclozolin was
observed among sixteen additional yeast isolates representing four species of Rhodotorula. The combination of yeast, vinclozolin and B. cinerea significantly reduced in vitro germination of B. cinerea conidia and growth of R. glutinis PM4. Incorporation of fungicides such as vinclozolin, into biocontrol mixtures, could help provide more consistent management of B. cinerea on ornamental plants
Impacts
Recently it was suggested that recommendations for managing Botrytis blight on ornamental crops in greenhouses in the Southeastern U.S. should de-emphasize the use of thiophanate-methyl, vinclozolin, and chemically related compounds due to the low incidence of isolates still sensitive to these fungicides. Use of yeast biocontrol in conjunction with vinclozolin could potentially allow for continued or even increased use of this fungicide on ornamental crops. The enhancement of yeast biocontrol activity by vinclozolin needs to be further tested against additional B. cinerea isolates, in scaled-up greenhouse trials with natural populations of the pathogen, and on different ornamental crops.
Publications
- Buck, J.W. 2004. Combinations of fungicides with phylloplane yeasts for improved control of Botrytis cinerea on geranium seedlings. Phytopathology 94:196-202.
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Progress 01/01/02 to 12/31/02
Outputs
The influence of inoculum and nutrient concentrations on the in vitro antagonism of Botrytis cinerea by phylloplane yeasts was investigated with detached leaf disk and conidial germination assays. Rhodosporidium toruloides Y-1091 significantly reduced lesion development after 96 h on geranium leaf disks when co-inoculated at 1 x 106 or 1 x 107 yeast cells mL-1 with B. cinerea conidia at 1 x 104 or 1 x 105 conidia mL-1. No effect on lesion development was observed when yeast and fungus were co-inoculated at a 1:1 ratio. Biocontrol activity of R. toruloides was greatest in 20 mM glucose and 20-fold dilute yeast nitrogen base. Twenty-five phylloplane yeasts exhibited a wide range of biocontrol activity when screened for antagonism of B. cinerea on geranium leaf disks (1 x 106 yeast cells mL-1, 1 x 105 conidia mL-1). Lesion development was significantly reduced by yeasts initially identified as poor antagonists when inoculated at higher concentrations (5 x 106 or 1 x 107
yeast cells mL-1) with B. cinerea. Both poor and good antagonists significantly reduced in vitro germination of B. cinerea conidia. The presence of B. cinerea conidia had a greater effect on the growth of two poor antagonists compared to two good antagonists on leaf disks. These data suggest that many phylloplane yeasts will antagonize B. cinerea under conditions of low nutrient availability and with high antagonist-to-pathogen ratios. The effects of fungicides on population size and the development of fungicide resistance in the phylloplane yeast flora of bentgrass was investigated. In spring of 2001, azoxystrobin, chlorothalonil, flutolanil, propiconazole were applied separately over a six week period to creeping bentgrass (Agrostis palustris Huds.). Total and fungicide-resistant yeast populations were assessed by dilution plating onto either potato dextrose agar (PDA) or PDA amended with the test fungicides. Total yeast populations in the fungicide treated plots were significantly
lower than the check plots on three out of four sample dates. In the fall, azoxystrobin or propiconazole were applied twice to the bentgrass over three weeks. Significantly larger total yeast populations were observed compared to resistant or highly resistant populations for each treatment on every sample date. Total yeast populations were significantly higher in the check plots compared to either the propiconazole or azoxystrobin treated plots on the first three of five sample dates. A collection of yeasts (N=114) with no prior exposure to fungicides were more sensitive to chlorothalonil, propiconazole, flutolanil, and iprodione than a second group (N=115) isolated from fungicide treated turfgrass. These results suggest that fungicide resistance among phylloplane yeasts is widespread and could be an important factor in the development of biological control agents for turfgrass diseases.
Impacts
Incorporation of biological control agents into management strategies for foliar disease control on ornamental plants would reduce grower's reliance on traditional fungicide chemistries.
Publications
- Buck, J.W., and Burpee, L.L. 2002. The effects of fungicides on the phylloplane yeast populations of creeping bentgrass. Can. J. Microbiol. 48:522-529
- Buck, J.W. 2002. In vitro antagonism of Botrytis cinerea by phylloplane yeasts. Can. J. Bot. 80:885-891.
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Progress 01/01/01 to 12/31/01
Outputs
Saprophytic yeasts are a common component of the mycoflora of aerial plant surfaces, including bark, leaves, and fruit surfaces, and are thought to provide a natural antagonistic buffer against fungal plant diseases. The antagonistic activity of various epiphytic yeasts against fungal pathogens has been utilized for the control of several post-harvest diseases of fruit. Incorporating the use of yeasts into the control of foliar diseases of ornamental plants requires a better understanding the nutritional and environmental effects on this antagonism and the impact of cultural practices on phylloplane yeast populations. Twenty-four phylloplane yeasts exhibited a wide range of biocontrol activity when screened for antagonism of B. cinerea on geranium leaf disks (1 x 106 yeast cells mL-1, 1 x 10-5 conidia mL-1). Lesion development was significantly reduced by all yeasts at higher concentrations (5 x 10-6 or 1 x 10-7 yeast cells mL-1). All yeasts significantly reduced in
vitro germination of B. cinerea conidia. The presence of B. cinerea conidia had a greater effect on the growth of two poor antagonists compared to two good antagonists on leaf disks. These data suggest that most phylloplane yeasts will antagonize B. cinerea under conditions of low nutrient availability and with high antagonist-to-pathogen ratios. The effects of fungicides on population size and the development of fungicide resistance in the phylloplane yeast flora of bentgrass was investigated. In spring of 2001, azoxystrobin, chlorothalonil, flutolanil, propiconazole were applied separately over a six week period to creeping bentgrass (Agrostis palustris Huds.). Total and fungicide-resistant yeast populations were assessed by dilution plating onto either potato dextrose agar (PDA) or PDA amended with the test fungicides. Total yeast populations in the fungicide treated plots were significantly lower than the check plots on three out of four sample dates. In the fall, azoxystrobin or
propiconazole were applied twice to the bentgrass over three weeks. Significantly larger total yeast populations were observed compared to resistant or highly resistant populations for each treatment on every sample date. Total yeast populations were significantly higher in the check plots compared to either the propiconazole or azoxystrobin treated plots on the first three of five sample dates. A collection of yeasts (N=114) with no prior exposure to fungicides were more sensitive to chlorothalonil, propiconazole, flutolanil, and iprodione than a second group (N=115) isolated from fungicide treated turfgrass. These results suggest that fungicide resistance among phylloplane yeasts is widespread and could be an important factor in the development of biological control agents for turfgrass diseases.
Impacts
Incorporating yeasts as biocontrol organism to manage foliar diseases of ornamental plants will help reduce the reliance on chemical controls.
Publications
- Buck, J. W. 2001. Will most phylloplane yeasts out-compete Botrytis cinerea for nutrients? Phytopathology 91:S12.
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Progress 01/01/00 to 12/31/00
Outputs
Botrytis blight-caused by the fungus Botrytis cinerea is a constant threat to plants grown in greenhouses. Many species of ornamental plants are susceptible to infection by B. cinerea, including important floriculture crops like African daisy, chrysanthemums, Exacum, geraniums, New Guinea impatiens, and poinsettias. Potential alternatives to traditional fungicides include the use of leaf surface yeasts as biological control agents. This study was conducted to determine if leaf surface (phylloplane) yeasts will reduce lesion development by B. cinerea. Thirty yeasts were isolated from the phylloplane of various ornamental plants and screened for antagonism of B. cinerea using a geranium leaf disk assay. Two-thirds of the yeast isolates significantly reduced lesion development after 4 days when co-inoculated with B. cinerea (1,000,000 cells ml-1 yeast and 10,000 cells ml-1 Botrytis). Reduction in lesion development ranged from 5 to 80% of controls. However, all isolates
significantly reduced lesion development when inoculum concentrations of the yeasts were increased tenfold. Reduction in lesion development was closely associated with the nutrient concentration of the inoculum. Increased antagonism was observed with decreasing concentration of carbon source. No reduction in lesion development by the yeasts was observed when glucose concentrations were above 40 mM. Lesion development by B. cinerea alone was greatly reduced or not observed when glucose concentrations were below 1 mM. Additional evaluations of the yeasts will be done on whole leaf/plant level in the greenhouse. Environmental and nutritional factors that might affect the growth and survival of yeasts on the foliage of various ornamental plants will be investigated.
Impacts
Although new fungicides have been developed in recent years for the control of Botrytis cinerea, non-chemical alternatives to fungicides, which would fit into an integrated management strategy for Botrytis blight, are needed. The use of antagonistic yeasts for biological control on ornamental plants would provide an alternative to traditional chemicals.
Publications
- No publications reported this period
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